1. Field of the Invention
The present invention relates generally to silencers and particularly to silencers used for example for internal combustion engines mounted in automobiles and the like.
2. Description of the Background Art
Vehicles and the like having an internal combustion engine or the like as a power source have a silencer mounted therein for the purpose of reducing noise caused by the internal combustion engine or the like.
The silencer is located under a floor of the vehicle. Accordingly, it is required to be more oblate as seen in cross section in order to ensure a sufficient cabin space and a minimal required spacing from the ground. It has been known, however, that such oblate geometry provides an increased area of a planar geometry of an outer cylinder and hence facilitates membrane vibration, resulting in disadvantageously increased radiating noise.
To address this, Japanese Utility Model Laying-Open No. 04-087312 proposes to provide an oblate outer cylinder with a reinforcement member along the cylinder's minor axis to enhance the cylinder in stiffness to reduce or prevent membrane vibration to reduce radiating noise.
Japanese Patent Laying-Open No. 2005-016494 proposes to provide an outer cylinder with a curving recess and protrusion to enhance the cylinder in stiffness to reduce or prevent the membrane vibration of the cylinder to reduce radiating noise.
The silencer described in Japanese Utility Model Laying No. 04-087312, however, has the reinforcement member and the silencer formed of discrete components, respectively. As such, it is difficult to sufficiently reduce or prevent the membrane vibration of the cylinder.
Furthermore, the silencer described in Japanese Patent Laying-Open No. 2005-016494 that has the outer cylinder provided with a curved geometry has a reduced capacity and hence muffles an insufficient amount of noise.